Zeolite Phi is defined and the method for its synthesis described in detail in U.S. Pat. No. 4,124,686, issued Nov. 7, 1978, to R. W. Grose et al. As disclosed therein, zeolite Phi is prepared hydrothermally from aqueous gels in the [N(CH.sub.3).sub.2 O--Na.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 system. As synthesized, the zeolite exhibits large pore adsorption characteristics, has a composition expressed in terms of molar oxide ratios as EQU 1.0.+-.0.5 Na.sub.2 O : 0.02-0.05 R.sub.2 O : Al.sub.2 O.sub.3 : 4-7 SiO.sub.2 : 0-6 H.sub.2 O
wherein "R" represents the tetramethylammonium ion, and has a characteristic x-ray powder diffraction pattern containing at least the d-spacings shown in Table A below.
TABLE A ______________________________________ Interplanar Spacing d,A Relative Intensity ______________________________________ 11.6 .+-. 0.2 M 9.5 .+-. 0.2 S 7.00 .+-. 0.15 S 5.61 .+-. 0.10 S 5.04 .+-. 0.08 S 4.31 .+-. 0.08 S 3.43 .+-. 0.06 VS 2.92 .+-. 0.05 VS 2.61 .+-. 0.05 W 2.09 .+-. 0.05 W ______________________________________
In the expression of the relative intensity values, VS=very strong, S=strong, M=medium and W=weak. Evidence supporting the large-pore status of zeolite Phi includes adsorption data for (C.sub.4 F.sub.9).sub.3 N and neopentane, the latter being adsorbed on a calcined template-free zeolite Phi in an amount of 3.5 weight percent at a temperature of 25.degree. C. and a pressure of 750 torr. These data can be interpreted to mean that zeolite Phi contains 12-membered oxygen rings, a proposition further supported by data reported by Martens and Jacobs (ZEOLITES, 1986, vol. 6, September) derived from the bifunctional conversion of n-decane using Pt-loaded hydrogen forms of zeolite Phi. It is observed that in the x-ray diffraction pattern of the zeolite a number of the diffraction lines are broadened, suggesting a high degree of disorder in certain crystallographic directions and making a detailed elucidation of the crystal structure impossible.
The synthesis and properties of zeolite Phi have been investigated on at least three other occasions, namely by P. A. Jacobs et al in 1987 (Stud. Surf. Sci. Catal. 1987, 33 at page 15 et seq.), H. Y. Li et al in 1990 as reported in Shiyou Huagong (Petroleum Chemical Engineering), vol. 19, No. 3, pgs. 148-152, and M. J. Franco et al in 1990, published in ZEOLITES, 1991, Vol. 11, April/May, pgs. 349-355. In the Jacobs et al study, it was reported that a zeolite Phi composition was prepared in an attempt to synthesize zeolite ZSM-20 using tetraethylammonium hydroxide (TEAOH) as the templating agent and a gel having the following composition: EQU [(TEA).sub.2 O].sub.9.3 (Na.sub.2 O).sub.1.1 (Al.sub.2 O.sub.3).sub.1.0 (SiO.sub.2).sub.20.0 (H.sub.2 O).sub.558
The silica reagent was hydrolyzed tetraethylorthosilicate from which the hydrolysis by-product ethanol was removed, and sodium aluminate was the source of alumina and a portion of the sodium. The remainder of the sodium was provided by NaOH. The gel was aged at 4.degree. C. (277.degree. K.) for 2 days and then autoclaved quiescently at 100.degree. C. for 14 days. Only the framework infrared data for the actual Phi composition prepared by Jacobs et al is reported. Presumably, except for the presence of the TEA.sup.+ cations rather than TMA.sup.+ cations, the physical and chemical properties of the Jacobs et al composition were essentially the same as those reported in the same article for the zeolite Phi of Grose et al.
In the work reported by Franco et al, supra, the authors employed synthesis gels in the system EQU (TEA).sub.2 O--Na.sub.2 O--K.sub.2 O--SiO.sub.2 --Al.sub.2 O.sub.3 --H.sub.2 O
The gels were prepared by the addition at room temperature of tetraethylorthosilicate (TEOS) to a stirred solution containing NaOH, NaAlO.sub.2, NaCl, KCl and TEAOH. After hydrolysis of the TEOS, stirring was continued for several hours to evaporate the ethanol formed. The resulting gels were then crystallized under static conditions at 100.degree. C. or 120.degree. C. for periods of 8 to 13 days. Of the six products which were relatively free of extraneous crystalline phases such as gmelenite, offretite and gismondine, the Si/Al.sub.2 ratios were within the range of 4.14 to 6.28. The Si/Al.sub.2 ratio in each instance was a consequence of a combination of the relative proportion of Na.sub.2 O, K.sub.2 O and TEAOH and the temperature at which the crystallization was carried out. With a total absence of potassium in the synthesis gel, an acceptable zeolite Phi composition was not produced, giving rise to the supposition by the investigators that in fact potassium was present in the Jacobs et al reaction mixture by virtue of being an appreciable impurity in the TEAOH reagent employed. The combined K.sup.+ +Na.sup.+ content of the TEAOH reagent employed by Franco et al was less than 20 ppm(w).
The x-ray powder diffraction pattern of the most crystalline zeolite Phi product of the Franco et al study is set forth in Table B, below. The radiation was CuK.sub..alpha..
TABLE B ______________________________________ d(.ANG.) I/I.sub.o .times. 100 ______________________________________ 11.5 .+-. 0.3 5 9.3 .+-. 0.2 24 6.9 .+-. 0.1 15 5.53 .+-. 0.08 16 5.01 .+-. 0.06 27 4.31 .+-. 0.04 66 3.97 .+-. 0.04 9 3.86 .+-. 0.03 13 3.77 .+-. 0.03 4 3.58 .+-. 0.03 22 3.14 .+-. 0.03 24 3.23 .+-. 0.02 8 2.92 .+-. 0.02 100 2.69 .+-. 0.02 5 2.60 .+-. 0.01 25 2.50 .+-. 0.01 10 2.30 .+-. 0.01 7 2.08 .+-. 0.01 15 ______________________________________
In general in the x-ray diffraction data appearing herein the relative intensity values reported in terms of numerical values of I/I.sub.0 .times.100 correspond to the commonly used expressions VS, S, W, etc., in the following manner:
______________________________________ Very Strong (VS) = 90-100 Strong (S) = 39-89 Medium (M) = 21-38 Medium-Weak (MW) = 13-20 Weak (W) = 1-12 ______________________________________
In contrast to the zeolite Phi compositions of Grose et al and the products attributed to Jacobs et al, the Phi products of Franco et al had adsorption properties characteristic of small to medium pore zeolites rather than large pore zeolites. This difference was attributed to stacking faults in the crystalline lattice.
The investigation of Li et al involved primarily synthesis gels in the TMA.sub.2 O--Na.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 system, although it is reported that zeolite Phi could be prepared using TEAOH, tetrabutylammonium hydroxide (TBAOH), propylamine or tripropylamine as the templating agent. In the experiments reported, attempts were made to determine the effects of a number of synthesis variables including changes in the TMAOH/SiO.sub.2 ratio, the SiO.sub.2 /Al.sub.2 O.sub.3 ratio, the Na.sub.2 O/SiO.sub.2 ratio, the H.sub.2 O/SiO.sub.2 ratio and the effects of different templating agents, and sources of Al.sub.2 O.sub.3 and SiO.sub.2. The correlations of the crystallization temperatures, at 120.degree. C., 100.degree. C. and 80.degree. C., with the crystallization rates and incubation periods for zeolite Phi production were also examined, but no observations concerning the correlation of crystallization temperature with the Si/Al.sub.2 ratio of the product zeolite were made. The Si/Al.sub.2 ratio of the zeolite Phi products reported were within the range of 3.3 to 3.9 and exhibited large pore zeolite adsorption properties as evidenced by the adsorption of appreciable quantities of tri-n-propylamine. All of the zeolite Phi materials produced were said to have thermal stability too poor for practical applications.